WATERTOWN, Mass. -- "Don't approach the subjects. Wait for backup."
That was the terse reply to Watertown police Officer Joe Reynolds from a dispatcher when he radioed that he was tailing a black SUV.
But Reynolds would soon learn that waiting for backup was not an option. When he followed the SUV onto Laurel Street just before 1 a.m. on April 19, 2013, the driver stepped out and began shooting and flinging bombs, setting off a lethal, chaotic chain reaction that would end the days long manhunt for the Boston Marathon bombing suspects.
When backup did arrive, the resulting firefight exposed a sobering truth about law enforcement. Sometimes too many guns and officers are worse than too few.
The early morning shootout cascaded out of a pair of crimes the preceding evening in neighboring Cambridge, only a few hours after authorities had released the photos of two men they believed were responsible for the Boston Marathon bombings three days earlier, which had killed three people and wounded more than 260.
At 10:20 p.m., police radios crackled with the news that a campus police officer at the Massachusetts Institute of Technology had been killed. Sean Collier was shot five times as he sat in his patrol car, and whoever shot him had tried unsuccessfully to steal the gun from his holster.
MIT via Getty Images file
MIT campus police officer Sean Collier, 26, was shot and killed during during an altercation with Boston Marathon bombing suspects Dzhokhar A. Tsarnaev, 19, and his his brother, Tamerlan Tsarnaev, 26, in Cambridge, Massachusetts.
Shortly after midnight, police radios came alive again. Officers were asked to keep their eyes out for a black 2013 Mercedes SUV. Two men of "Middle Eastern" appearance had carjacked the owner and taken him hostage. When they stopped for gas at a station in Cambridge just after midnight, the captive had escaped and called 911. He said the men were talking about heading to New York.
Police tracked the Mercedes SUV via GPS as it headed west into the suburb of Watertown, down dark, leafy streets lined with single-family homes. Reynolds picked up the trail of his SUV and followed with his lights off.
"My officers truly believed they were going to stop that car," said Watertown Police Chief Ed Deveau, "two teenage kids were going to jump out of it, and they were going to chase them through the backyards."
Uncredited / FBI via AP
This image released by the FBI on Thursday, April 18, 2013, shows in a image from video what the FBI are calling suspect number 1, front, in black cap, and suspect number 2, in white cap, back right, walking near each other through the crowd in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon.
But Tamerlan Tsarnaev, the 26-year-old Russian Muslim immigrant whose picture had just been shown on television as the unnamed "Suspect 1" in the marathon bombings, was driving the SUV. And just in front of that vehicle, "Suspect 2" -- Tamerlan's 19-year-old brother, Dzhokhar -- was driving a green Honda.
The Tsarnaevs pulled their cars on to a short block of Laurel Street, driving east, and Reynolds, alone in his patrol car, followed. Then, suddenly, just before the corner, Tamerlan hit the brakes on the SUV, stepped out of the driver's side brandishing a Ruger, and began walking towards Reynolds, firing his weapon.
Reynolds slammed his patrol car into reverse and backed up 30 yards, just as Watertown Police Sgt. John MacLellan arrived on the scene in his own radio car.
When Tsarnaev turned his gun on MacLellan, the sergeant put his cruiser in drive, hopped out with only his service pistol and sent it rolling toward the Tsarnaev brothers to draw fire. He began yelling into the radio, "Shots fired! Shots fired!"
'They're throwing bombs at us.'
The suspects now revealed they had other weapons in their arsenal. Some kind of homemade device came flying at the officers and exploded when it hit the pavement. It was an exact replica of the nail-stuffed pressure cooker bombs that had torn the flesh from spectators at the marathon that Monday.
"Chief, they're shooting. They're throwing bombs at us," Reynolds told Deveau. "And I think these are the guys that killed the MIT officer."
Other Watertown officers were pulling up at the scene as more bombs came flying from the east end of Laurel Street. One, Jeffrey Pugliese began moving toward the Tsarnaev brothers on the northern side of Laurel, in a classic flanking maneuver.
With police dispatchers throughout the region now involved in marshalling a response, soon cops, state troopers and federal agents -- representatives of more than a dozen separate agencies in all -- began descending on Laurel Street.
Some of the officers were already part of the investigation, or had been dispatched. Others "self deployed," meaning they were volunteers, unknown men with guns who arrived unannounced in the middle of a shootout. By the end of the shootout, there was even a National Guardsman in tan fatigues and helmet on nearby Mt. Auburn Street.
"The cavalry came," said Deveau. But no one was leading the charge.
Courtesy of Andrew Kitzenberg
Andrew Kitzenberg watched as two people, later known to be the Tsarnaev brothers, take cover behind an SUV and engage in gunfire with authorities. The shootout was followed by an overnight citywide manhunt.
In effect, the suspects ended up at the center of a ring of cops on Laurel Street between Dexter and School streets during the 20-minute firefight, and the bullets that were fired at them often hit near the officers on the other side.
"Certainly not a good idea," said Davis. "They see somebody shooting, so they fire at them. That's their training."
Police training dictates that officers consider several key factors when making the decision to fire their weapons. They must assess the danger posed to bystanders, residents and fellow officers, they should know the position of fellow officers and they should stop to reassess the situation if they can, rather than simply continuing to pull the trigger.
But on Laurel Street, rounds flew into parked cars and police vehicles and chewed up fences and trees. A round entered the home of Andrew Kitzenberg on the north side of the street and lodged in a chair. Another ripped through the exterior wall of Adam Andrew and Megan Marrer's house and landed on their living room floor.
More than a dozen officers suffered minor injuries during the mayhem, but none was believed to have been wounded by the suspects. The only serious wound was suffered by Richard Donohue, a transit cop with the Massachusetts Bay Transportation Authority, who was hit in the groin by a police bullet and began to bleed profusely.
A bullet scar on a tree near where the Tsarnaev brothers' vehicles stopped on Laurel Street in Watertown, Mass., at the outset of a firefight with police on April 19, 2013.
The suspects, meanwhile, had not surrendered. Twenty minutes into the firefight, however, Tamerlan Tsarnaev left the shelter of the SUV and began walking toward Watertown police Sgt. Jeff Pugliese.
"It absolutely felt like it was something from a movie," said local resident Andrew Kitzenberg, who watched - and filmed - some of the action from inside his Laurel Street home. "He was charging them and engaging them in gunfire."
Tamerlan, though wounded, kept walking toward Pugliese until his gun jammed or he ran out of ammo. Then he threw the weapon at Pugliese, hitting him in the arm, and turned to run back to his vehicle.
"Jeff, you know, without any regard for his own safety, started to bring this shootout to an end," said Deveau.
Seizing his chance, Pugliese tackled Tamerlan in the street. A group of officers held the suspect down to cuff him.
Then Tamerlan's younger brother Dzhokhar jumped into the SUV, swung it around in a U turn, and began accelerating toward the clot of officers hovering over his brother. The officers jumped out of the way. Tamerlan didn't. The SUV ran over Tamerlan and dragged him 25 to 30 feet, and then swung out onto Dexter and vanished into the night.
The Lowell Sun & Robin Young via AP; FBI file
Tamerlan Tsarnaev, 26, left, and Dzhokhar Tsarnaev, 19.
Dzhokhar Tsarnaev was able to flee in part because the officers who knew the streets best, the Watertown cops, were tending to Donohue, but also because the mob of "self-deployed" officers had created an obstacle course of vehicles. He weaved through them before any of them could react.
There was a 45-second lag, according to witnesses, before cars gave pursuit without success. After a mistaken police radio report that Tsarnaev had stolen a state police SUV, however, multiple rounds were fired at a state police vehicle that was leaving the scene. No one was injured. Officers, guns drawn, also briefly surrounded an innocent pedestrian and the innocent driver of a vehicle near the scene.
The same gridlock of cars delayed the emergency vehicles en route to pick up Richard Donohue and transport him to a hospital. He survived despite massive blood loss.
When the shooting was over, police had fired at least 100 rounds. The exact number has never been released. There was a small pile of shells near the bloody spot on the pavement where Tamerlan's body had come to rest after being dragged by the SUV. Witnesses said they'd seen officers shooting at him on the ground. He was pronounced dead at a nearby hospital.
A stain marks the asphalt on Laurel Street in Watertown, Mass., where Tamerlan Tsarnaev was run over and dragged by the SUV allegedly driven by his younger brother, Dzhokar.
The suspects might not have done much shooting at all. They had thrown as many as a half-dozen homemade bombs at the officers, including several duds, but were found to have had only one gun between them. They may have fired fewer than 10 shots total.
Eighteen hours later, the police caught up with Dzhokar Tsarnaev. Once again, cops and guns crowded the stage, even jostling for position, and once again that led to an excess of bullet casings on the ground.
The Boston metro area was locked down by Massachusetts Gov. Deval Patrick all day on Friday, April 19, as cops searched Watertown for the missing suspect. They'd found both the Honda and the SUV abandoned near the site of the Laurel Street shootout, and believed that Dzhokhar might be nearby, wounded and hiding.
At 6:07 p.m., Patrick ended the lockdown. A resident of Watertown's Franklin Street, just a few blocks west of Laurel and Dexter, went outside to get fresh air and fix the covering on his boat. It had somehow come loose and had been flapping in the wind, and it bugged him.
When he looked under the tarp and inside the boat, he saw blood, and the figure of a man huddled by the engine block. He ran back inside and called 911.
"Almost immediately," says a Harvard report on the Marathon manhunt, "a senior police officer was on the scene, establishing incident command and requesting 'a tactical team' for support. He got much more than he asked for."
The senior commander at the scene, William Evans, is now commissioner of the Boston Police Department. The man he succeeded, Ed Davis, also was at the scene, coordinating with the FBI's hostage rescue team for a period of time.
Officers from the Boston PD, Watertown PD, the state police and various tactical units surrounded the boat.
The commander on scene was able to deploy the tactical team and establish a perimeter, says the report, but his control was only partial because there were so many extra, "self-deployed" bodies arriving.
A member of one SWAT team tried to take up a position on a rooftop, only to find that a member of a different SWAT team was on the same roof. After an argument, neither man would budge.
At around 7 p.m., a voice on the police radio issued a warning, "There's a perp in the boat trying to poke a hole in the liner, a perp in the boat. Live party who may be trying to object out, live party in the boat confirmed."
Tsarnaev was pushing a long, thin object up through the boat covering. The object later turned out to be a fishing gaff, which Tsarnaev may have been trying to use to push up the tarp so he could see out.
But one of the snipers on the roof saw the object and began shooting. It sparked a round of what is known as "contagious fire," where other officers with their fingers on the trigger began peppering the boat with bullets.
The commander began shouting for the officers to cease fire, but the fusillade went on for 10 seconds. Hundreds of rounds were expended.
When the shooting stopped, order was restored. The FBI's hostage rescue team used a robotic arm to pull the wrapping off the boat. Flash grenades thrown at the craft were meant to stun Tsarnaev, and he was urged via bullhorn to surrender.
Sean Murphy / AP file
Boston Marathon bombing suspect Dzhokhar Tsarnaev leans over in a boat at the time of his capture by law enforcement authorities in Watertown, Mass. He had been hiding in the boat after a days-long manhunt for the two bombing suspects.
Tsarnaev ultimately emerged from the boat, wounded and bloodied. He had somehow survived two separate firestorms of bullets in less than 24 hours. Red dots from laser sights appeared all over his body as officers aimed their weapons, safeties off.
But no one fired, and Tsarnaev surrendered. Officers laid him on the lawn. At 8:42 p.m, officers reported via radio that the suspect in custody.
Ed Davis, the former Boston police commissioner, declined to fault the cops who took part in the shootout and subsequent hunt for Dzhokar Tsarnaev, but he acknowledged that the need to better prepare officers for such chaotic scenes.
"The officers that responded there did exactly the right thing. No one is—criticizing them. And don't take any of my statements to think that I think that anybody did anything wrong," he said. "But it's important to learn from anything that happens, and I think that … has to be factored into ongoing training."
No weapon was found on Tsarnaev's body or in the boat. He was taken to a hospital and has since recovered from his wounds. He faces prosecution on terrorism charges that carry a potential death penalty.
Geoff Alpert, a criminology professor at the University of South Carolina, said that even accounting for the circumstances of the bombing and the firefight in Watertown, the showdown with the Tsarnaev brothers highlights troubling shortcomings for Boston-area law enforcement in overall preparedness for large-scale tactical incidents.
"Someone has to be in charge."
"There should have been protocols in place that night and the analogy is a fire," Alpert said. "Firefighters and firetrucks are not going to just show up and start spraying each other. Each group is going to have is going to have a responsibility and someone is going to coordinate among those groups. Police work is no different, except the consequences can be even more disastrous for not having general, pre-established procedures before the chaos hits.
"There might be breakdowns and people might make decisions on less information than they would like in less than ideal conditions, but someone has to be in charge. Otherwise, you have all these individuals making decisions on very limited information and on very limited resources instead of pooling them."
Scott Reitz, a former LAPD SWAT unit member and a national firearms tactics and deadly force expert, said that most officers act "with the best of intentions," and that the "confusion, misdirection and overall chaos" of an incident like Watertown can't be understated, especially weighed against the limitations of training vs. real-world experience.
"In essence, it would be analogous to practicing on a stick-shifted Volkswagen Bug and then being thrown into the Le Mans in a Formula One racecar, at night, in the rain," Reitz said. "One cannot train to one level of proficiency when an entirely different level is required in the real world. The results are somewhat predictable."
In his experience, Reitz said that sometimes less is more when it comes to engaging suspects.
"Having trained many tens of thousands of officers from around the world over many decades, I continually stress that it is equally important if not more so, to know when not to shoot - as it is when to shoot." he said.
Follow NBC News Investigations on Twitter and Facebook.
First published April 15 2014, 12:48 AM